1. Field of the Invention
The present invention relates generally to switch devices for switching the positions of railway tracks in order for trains to move from one track to another. More particularly, the present invention relates to a gear box having a low vertical profile, to be used in an electric motor driven switch machine.
2. Description of the Related Art
It is a requirement for operation of a railroad network to have the capability of switching railroad trains from one track to another. A common method of providing this switching capability is to install an electric motor driven switch machine alongside of, and interconnected to, a switch point of a railroad track. These switch machines often have one or more manual operations for shifting the position of the track without the use of the electric motor for certain situations, such as when electric power is not available.
Two manual operations typically integrated within switch machines are the hand crank and hand throw operations. The hand crank operation permits operational personnel to switch the track at the switch point by turning a hand crank for maintenance and installation purposes. The handthrow operation permits operational personnel to switch the track, i.e., throw the switch machine, at the switch machine when control signals from a remote control facility are not able to reach the switch machine.
Conventional design practice has been to place hand throw means for controlling the handthrow operation above one of the drive shafts of the switch machine, such as the crankshaft. This practice not only creates an undesirable bump in the top profile of the machine, but also contributes to the high vertical profile of existing machines. However, this practice does in fact provide a simpler gear box with fewer components than when the hand throw means is not located above one of the drive shafts, as in the related art low profile switch machine disclosed in U.S. Pat. No. 5,494,242, issued in the name of Ludwick et al. and further described below. A lower profile gear box mounted on a typical switch machine assembly thereby to provide a lower vertical profile and no projections extending from its top surface is desirable for many applications. Particularly for transit applications it is essential that a low profile be maintained by a switch machine in order to clear a railway car clearance profile identified by steps, third rail electric pickups, and other types of ground clearing equipment extending down from a transit car or locomotive.
A low profile switch machine without overhead projection is also desirable for additional safety and maintenance reasons. The switch machine is subject to all manner of damage due to its harsh environment. For example, vehicles or objects that may contact and damage the switch machine include rail maintenance equipment, snow removal means, foreign objects falling off trains, local car and truck traffic in the area and other objects passing through or over the general vicinity of the switch machine.
FIG. 1 shows a top view of a related art gear box 100 for a typical switch machine manufactured by Union Switch & Signal Inc. of Pittsburgh, Pa., USA. FIG. 2 is a cross-sectional right view of a switch machine gear box taken along the line II--II of FIG. 1. As is known in the art, a hand throw shaft 105 may be rotated approximately 180.degree. by a hand throw lever 110 connected thereto. Similarly, an eccentric shaft 115 may be rotated approximately 180.degree. independently of and within the hand throw shaft 105 (refer to FIG. 2) by a selector lever 120 connected thereto. The hand throw shaft 105 and the eccentric shaft 115 are commonly retained by a hand throw bearing 122 affixed to one side of a housing 123. Typically, a blind side bearing 124 is affixed to an opposing side of the housing 123 and pivotally retains a clutch yoke 125 at a pivot pin 126.
When the selector lever 120 is positioned to the right of the gear box 100, as shown in FIG. 1, the gear box 100 is known to be in "power" mode since the clutch yoke 125 (see FIG. 2) lowers a clutch cup assembly 127 to engage a worm gear 130, thereby to drive the switch machine by a motor (not shown) connected to reduction gears 132, 134, 136 typically located in a reduction box 138.
The selector lever 120 may be rotated 180.degree. to the left of the gear box 100. When the selector lever 120 is positioned to the left of the gear box 100, the gear box 100 is known to be in "hand throw" mode since the clutch yoke 125 (see FIG. 2) raises the clutch cup assembly 127 to engage a top bearing bevel gear 145 that engages a large diameter hand throw bevel gear 147. When the gear box 100 is in hand position, rotation of the hand throw lever 110 rotates the hand throw bevel gear 147, and the hand throw bevel gear 147 rotates the top bearing bevel gear 145 and the clutch cup assembly 127, thereby to rotate a main crank shaft 150, thus operating "hand throw" mode of the gear box 100 in a manner known in the art. The large diameter hand throw bevel gear 147 typically requires the housing 123 to have a having a total working height H1, as shown in FIG. 2. The total working height H1 is typically in the range of about 9 inches.
FIG. 3 shows a partial cut-away side view of the clutch cup assembly 127, in accordance with the prior art. As is known in the art, the clutch cup assembly comprises an upper clutch 160, an upper clutch cup 164, a lower clutch 166, a lower clutch cup 170 and a clutch spring 172. The upper clutch 160 typically has a plurality of vertical teeth 162 and is slidably mounted about the main crank shaft 150 (see FIG. 2) along with the upper clutch cup 164 that cooperates with the upper clutch 160. Similarly, the lower clutch 166 typically has a plurality of vertical teeth 168 and is slidably mounted about the main crank shaft 150 (see FIG. 2) along with a lower clutch cup 170 that cooperates with the lower clutch 166. The clutch spring 172 typically is slidably mounted about the main crank shaft 150 and biases the upper clutch 162 and the upper clutch cup 164 away from the lower clutch 166 and the lower clutch cup 170. The clutch cup assembly 127 typically requires an assembly height H2, typically about 5.25 inches, and an assembly width W2, typically about 4.1875 inches. The assembly height H2 typically occupies a portion of the total working height H1.
Because a switch machine may be mounted on either the left hand or the right hand side of the track, the hand throw lever 110 and the selector lever 120 must be capable of being moved from one side of the gear box 100 to the other, thereby to accommodate a left side and a right side configuration. Commonly known gear box designs, such as the design of FIGS. 1-2, typically require that the entire gear box 100 be disassembled and then reassembled in order to accomplish the movement from one side of the gear box 100 to the other. As may be seen best by referring to FIGS. 1-2, conversion of the hand throw shaft 105 and the eccentric shaft 115 from the left side of FIG. 2 to the right side requires disassembly and then reassembly of at least the hand throw bearing 122, the blind side bearing 124, the hand throw shaft 105, the eccentric shaft 115, the clutch yoke 125, the pivot pin 126, the clutch cup assembly 127, the top bearing bevel gear 145, and the hand throw bevel gear 147. Typical conversion time may be greater than one hour and may require a wide variety of tool, including several open-end wrenches, screwdrivers, socket wrenches, pliers, etc.
Additionally, as viewed in FIG. 2, the total working height H1 of the gear box 100 commonly prevents the switch machine from being mounted close to the railroad tracks, and the machine mounting ties typically require cutting or dapping to lower the switch machine with respect to the top of the rail, thereby to stay below the car clearance line to avoid interference with moving railroad cars and equipment.
In the Ludwick reference, a switch machine for railroad tracks is provided having a low vertical profile without increasing the axial length of existing switch machines. Also, the capability of being operated by an electric motor, handcrank, or handthrow operation has been retained within the new dimensional constraints. A particular electric motor and gear box combination permits a low overall profile due to its compact size. The Ludwick reference describes that a worm gear shaft serves the dual purpose of driving a worm wheel and coupling to a handcrank, thus maintaining the low profile while increasing the functionality of the shaft. In addition a handthrow drive shaft is provided adjacent to a crank drive shaft in order to provide a handthrow operation while further maintaining the low profile of the switch machine. It is noted at Column 5, lines 37-42 of the Ludwick reference that the apparatus of the Ludwick reference provides a third vertical shaft, i.e., the hand throw shaft, that is separate and horizontally adjacent to the crank shaft, thereby to reduce the vertical profile of the switch machine by four or more inches lower than existing switch machines. However, the handthrow and selector levers are not easily moved from one side of the switch machine to another without time-consuming disassembly and reassembly of component parts.
Consequently, a need exists for a switch machine gear box having a low profile (i.e. height) that reduces the overall working height of the switch machine to permit the switch machine to be mounted closer to the rail but still remain below the railroad car clearance profiles, and wherein the handthrow and selector levers may be more easily moved from one side of the gear box to the other, thereby to accommodate mounting the switch machine on either the left-hand or the right-hand side of the track.